As
scientific research on endocrine disruption has advanced, the scope
of the research has broadened significantly. The list
of hormonally active compounds is longer than anyone had previously
imagined in the early days of the research. Not only are more compounds
involved, but more hormone systems
are now known to be vulnerable. And within each hormonal system,
new mechanisms of interaction between compounds and receptor systems
are being explored to understand how a compound exerts its effects.
Research on leguminaceous
plants and their symbiotic rhizobial bacteria show that chemical
communication between organisms is also vulnerable to disruption
by contaminants.

New
compounds: Accidental discoveries and systematic testing have
revealed a broader array of modern use compounds capable of interfering
with the sex steroids hormones. New results
come in regularly, identifying yet another hormonally-active compound.

Most
notably, because of their ubiquity, certain compounds in plastics
began to attract attention, especially nonylphenol and bisphenol-A
(Our Stolen Future, Chapter 8). Nonylphenol is used widely
as a surfactant (for example, in pesticides
and detergents) and as an additive to certain plastics. Bisphenol-A,
the basic building block of polycarbonate plastic, not only enters
our lives in every objects made from polycarbonate, for example
clear plastic baby bottles, it also enters children's mouths when
their teeth are coated with polycarbonate to prevent cavities. And,
like nonylphenol, bisphenol-A is used as a surfactant in pesticides.
The ubiquity of exposure is breathtaking.

Concern
began to turn to phthalates in the late 1990s after studies
showed their potency as a reproductive toxicant during crucial windows
a development. The first issues raised were about their use as additives
to PVC plastics that make them flexible, and thus useful in children's
toys and medical devices, among many uses. But then in mid-2000,
the CDC opened a dramatic new chapter in the phthalate story with
convincing demonstration of the ubiquity
of phthalate contamination, and a particularly troubling
revelation for women of child-bearing age.

Even
bakelite (also known as bisphenol-F
), the first of the modern plastics, has been found to be estrogenic.
This pushes widespread exposure to synthetic estrogens back to
the first decade of the 20th century.

More
hormone systems: The initial concern in endocrine disruption
had focused on contaminants capable of interfering with the sex
steroid hormones, especially estrogen. Research emphasized the classic
estrogen mimics and antagonists--DES, certain PCBs, DDT, etc.

But hormone
disruption is not limited to estrogenic compounds nor the estrogen
receptor. To begin with, scientists have learned that there
is more than one estrogen receptor. Furthmore, the mechanisms of
disruption are diverse and complex; a compound may be an agonist
(mimicking the actions of a hormone) or antagonist (interfering
or blocking actions of a hormone); it
may alter transport of a hormone; or it may bind to more than
one hormone receptor. Research on the sex steroids has been broadened
to include anti-estrogenic and
anti-androgenic activities.

And,
because every hormone system is potentially vulnerable to disruption
or alteration, the list of hormone systems investigated has broadened
beyond the sex steriods. Scientists have begun to look at other
hormone signalling systems...thyroid,
progesterone, retinoids,
glucocorticoids,
etc. Compounds capable of interfering with each of these systems
have now been reported. And even though hormone disruptors have
not yet been identified for every hormone system, the lack of data
is most safely attributed to the diversity and sheer number of compounds
yet untested.

Perhaps
the most troubling aspect of many of these discoveries was their
accidental nature. Acknowledging this and also the strong likelihood
that many compounds might possess disruptive capabilities, the US
Congress in 1996, unanimously passed the Food Quality Protection
Act. FQPA established a new committee, the Endocrine Disruption
Screening and Testing Advisory Committee (EDSTAC),
to advise EPA on the development of a screening program that would
systematically survey a variety (i.e, 15,000) of modern day use
compounds whose effects on the endocrine system were virtually unknown.

Recent
discoveries:

EDCs
disrupt the
the symbiosis between legumes and Rhizobium, undermining nitrogen
fixation, a process essential for life on earth.

polybrominated
diethyl ethers (PBDEs) are steroid and thyroid
disruptors. They are used as flame retardants in many modern
consumer products. They are more persistent than PCBs and have
become ubiquitous contaminants throughout the world, including
in remote
ocean life.

soccer
shirts manufactured by a large consumer product firmcontain
tributyltin, an endocrine disrupting compound known to have
dramatic impacts on marine life.

methoprene
(a common active ingredient in insecticides) and the breakdown
products of methoprene interfere with retinoid
signalling.

Synthetic
pyrethroids, widely used to combate ticks, mosquitos and even
head lice, are powerful endocrine disruptors.